The present invention relates to the technical sector of small self-propelled machines for building sites, having hydrostatic drives.
In the site machines sector the heat developed by the hydrostatic drive during machine use is normally disposed of using heat exchangers, or radiators, mounted on the hydrostatic system itself and ventilated by ventilation means which may or may not be driven electrically by the service apparatuses with which the machine is usually equipped.
In machines of more simple construction which do not have electrical, ignition and service systems, in which the engine is started by a manual pull starter, such cooling is achieved by means of fans which operate in such a way that the outside of the pump body is struck by a flow of suitably accelerated air which produces forced convection against the pump body, which helps to cool the drive oil contained in it and/or passing through the pump body.
The first type of said solutions can be applied to machines with a medium high technological level and a corresponding price band. Obviously, the machine must have an electrical ignition system which can supply the electricity for accessory services provided in addition to the basic machine functions. Obviously, this already involves a certain basic cost of the machine which is not negligible. The machine must also be fitted with the exchanger and/or radiator with the ventilation means used by it, which contribute to a further rise in the overall price band of the machine.
In contrast, the second type of solution is characteristic of smaller, less expensive machines, and/or relatively low-powered machines in which the machine structure is designed in such a way as to keep the machine costs at the lowest possible values by excluding all apparatuses—for example the electrical ignition system—which are not strictly necessary to the minimum basic functions of the machine.
In this latter construction approach—which represents the prior art most relevant to the present invention—an embodiment is already known which involves the use of a fan for the pump body, which—with reference to the direction of travel of the vehicle—is located behind the internal combustion engine in the machine. The rotation of the fan is driven by a shaft driven by a mechanical belt drive which, in turn, is operated by the mechanical drive control which allows machine motion relative to the ground to be switched on or off.
However, such a solution, although spread with a certain degree of success on the market, is not without disadvantages.
Firstly, positioning the fan behind the engine means that the fan produces a ventilation flow with reduced cooling efficiency. The flow produced is subject to two heating effects, one because around the internal combustion engine the air is heated by the heat of the engine, and the other because the air passing from behind the engine towards the pump in front is inevitably forced to go through a zone directly influenced by the engine, and is further heated.
Another disadvantage is the fact that the ventilation system operates only when the vehicle is moving. In other words, when the vehicle is stationary, even with the internal combustion engine switched on, and therefore when the cooling effect of the wind from travel is completely absent, the cooling system of the hydraulic circuit cannot operate; that is to say, paradoxically, it does not operate precisely when it is most needed.
Another disadvantage is the presence of a mechanical drive inserted between the mechanical movement control and the ventilation system; a drive which, however simple, involves the presence of mechanical parts which have a negative effect on costs and the presence of interposed mechanisms, involving mechanical performance having a negative effect on the energy efficiency of the machine as a whole.